Lubricant composition



United States Patent 3,150,092 LUBRECANT COMPOSITION Daniel B.Eickemeyer, Park Forest, 111., and James E.

Engelking, St. Paul, Minn., assignors, by mesne assignments, to SinclairResearch, Inc, New York, N.Y., a

corporation of Delaware No Drawing. Filed June 9, 1%0, Ser. No. 34,882 2Claims. (Cl. 252-463) This invention relates to ester-based lubricantcompositions and more particularly to ester-based lubricant compositionscontaining phenothiazine and a base oilsolubleS-alkyl-lO,10-diphenyl-phenazasiline which have improved resistance tooxidation.

Organic compounds, such as lubricating oils, undergo oxidation uponexposure to air. This process is accentuated by elevated temperaturessuch as occur in engines and other operating machinery. When suchorganic compositions are used as motor or machinery lubricants, theirstability is still further drastically reduced due to their contact withmetal surfaces which give up metallic particles into the lubricant. Suchabraded or dissolved metals or metal salts appear to act as oxidationcatalysts in ,the lubricant causing the formation of primary oxidationproducts which in turn cause further degradation of the organiccompounds present in the composition. In addition, Water also causescorrosion of metallic surfaces and accentuates oxidation of thelubricant. Problems of this nature are encountered in mineral oils butappear to be particularly troublesome in synthetic oleaginous fluidsexemplified by esters. These synthetic fluids are not sufficientlyresistant to oxidation to be useful alone.

They can, however, be adequately protected by use of small amounts ofadditives. Phenothiazine has been employed extensively to protectsynthetic fluids against oxidation. Its activity, however, is not greatenough to protect fluids for long periods of time above about 400 F.

It is the particular object of the present invention to provide an esteroil of lubricating viscosity that exhibits increased resistance tooxidation. Further, the additives of the present invention have provenfar more effective than the conventional use of phenothiazine alone inreducing oxidation in synthetic ester fluids.

The present invention provides an improved esterbased lubricantcomposition containing phenothiazine and a-alkyl-l0,10-diphenyl-phenazasiline wherein the alkyl group is a loweralkyl group i.e. generally of about 1 to 4 carbon atoms, preferably 2carbon atoms. The rings of the latter compound may be substituted as forinstance with alkyl groups. The additives of the present invention areused in minor amounts that provide a final esterbased syntheticlubricant composition exhibiting increased.

resistance to oxidation under temperatures such as in excess of 400 F.The amounts added shouid be solublein the base oil into which they areintroduced and these amounts may vary'with the particular base oilutilized. Generally the 5alkyl-10,IO-diphenylphenazasiline component ofthis invention is added in amounts from about .01 to 5 percent by weightof the final composition'with a preferred amount being about-0.1 to 2percent by weight.

meta to the nitrogen. The relative concentrationstof the additives mayvarywith the particular ester lubricant,

employed and-also be dependent upon the characteristics of the finallubricant composition desired. Normally, it

preferably about 20 to 35 weight percent.

3,15%,(992 Patented Sept. 22, 1964 are made from monoand polyhydroxyaliphatic alco hols and aliphatic carboxylic acids, frequently of about4 to 12 carbon atoms; aliphatic including cycloaliphatic. The reactionproduct of a monohydroxy alcohol and a monocarboxylic acid is usuallyconsidered to be a simple ester. A diester is usually considered to bethe reaction product of 1 mole of a dicarboxylic acid say of 6 to 10carbon atoms with 2 moles of a monohydric alcohol of, for instance 6 to12 carbon atoms or of 1 mole of a glycol of 4 to 10 carbon atoms withtwo moles of a monocarboxylic acid of 4 to 10 carbon atoms. The diestersfrequently contain from 20 to 40 carbon atoms. One complex ester isusually considered to be of the type XYZY-X in which X represents amonohydric alcohol residue, Y represents-a dicarboxylic acid residue andZ represents a glycol residue and the linkages are ester linkages. Thoseesters, wherein X represents a monoacid residue, Y represents a glycolresidue and Z represents a dibasic acid residue are also considered tobe complex esters. The complex esters often have 30 to 50 carbon atoms.Polyesters, or polyester bright stocks can be prepared by directesterification of dibasic acids with glycols in about equimolarquantities. The polyesterification reaction is usually continued untilthe product has a kinematic viscosity from about 15 to 200 centistckesat 210 F, and preferably 40 to centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, theyare particularly useful when added or blended with each other insynthetic lubricant compositions. These esters and blends have beenfound to be especially adaptable to the conditions to which turbineengines are exposed, since they can be formulated to give a desirablecombination of high flash point, low pour point, and high viscosity atelevated temperatures, and need contain no additives which might leave aresidue upon volatilization. In addition, many complex esters have showngood stability to shear. Natural esters, such as castor oil may also beincludedin the blends, as may be up to about 1 percent or more by weightof a foam inhibitor such as a methyl silicone polymer or other additivesto provide a particular characteristic, for instance,

extreme pressure or load carrying agents, corrosion in-' plex ester atan elevated temperature, altering the proportions of each componentuntil the desired viscosity is reached. Polyesters can be employed tothicken diester base' stocks to increase the load carrying capacity ofthe base diester oil. The polyester will generally not comprise morethan about 50 weight percent of the blend,

amount of the polyester employed in any blend would be at least about 5percent, and the majority of the lubrif jcant is a diester. Otherpolymers such as the acryloids may be added as thickeners to the esters,generally the single esters to obtain a base oil of desired viscosity."

The acryloids are polymers of mixed C to C esters of methacrylic acidhaving a 16,000 to 20,000 molecular weight. Advantageously the finallubricating oil compo- 'sition would have a maximum viscosity at 40 F.of

Usually the F about 13,000 centistokes and a minimum viscosity of about7.5 centistokes at 210 F.

The monohydrice alcohols employed in these esters usually contain lessthan about 20 carbon atoms and are generally aliphatic. Preferably thealcohol contains up to about 12 carbon atoms. Useful aliphatic alcoholsinclude butyl, hexyl, methyl, iso-octyl, and dodecyl alcohols, C oxoalcohols and octadecyl alcohols. C to C branched chain primary alcoholsare frequently used to improve the low temperature viscosity of thefinished lubricant composition. Alcohols such as n-decanol, 2-ethylhexanol, oxo alcohols, prepared by the reaction of carbon monoxideand hydrogen upon the olefins obtainable from petroleum products such asdiisobutylene and C olefins, ether alcohols such as butyl carbitol,tripropylene glycol mono-isopropyl ether, dipropylene glycolmono-isopropyl ether, and products such as Tergitol 3A3, which has theformula C H O(CH CH O) H, are suitable alcohols for use to produce thedesired lubricant. If the alcohol has no hydrogens on the beta carbonatoms, it is nee-structured; and esters of such alcohols are oftenpreferred. In particular, the neo-C alcohol2,2,4-trimethyl-pentanol-l-gives lubricating diesters or givescomplex esters suitable for blending with diesters to produce lubricantswhich meet stringent viscosity requirements. Iso-octanol and isodecanolare alcohol mixtures made by the x0 process from C C copolymer heptenes.The cut which makes up iso-octanol usually contains about 17%3,4dimethylhexanol; 29% 3,5-dimethy1hexanol; 25% 4,5-dimethylhexanol;1.4% 5,5-dimethylhexanol; 16% of a mixture of B-methylheptanol and-ethylheptanol; 2.3% 4-ethylhexanol; 4.3% a-alkyl alkanols and 5% othermaterials.

Generaliy, the glycols contain from about 4 to 12 carbon atoms; however,if desired they could contain a greater number. Among the specificglycols which can be employed are 2-ethyl-l,3-hexanediol, 2-propyl-3,3-heptane-diol, Z-methyl-l,B-pentanediol, 2-butyl-1,3-butanediol,2,4-diphenyl-1,3-butanediol, and 2,4-dimesityl-1, 3-butanediol. Inaddition to these glycols, ether glycols may be used, for instance,where the alkylene radical contains 2 to 4 carbon atoms such asdiethylcne glycol, di propylene glycol and ether glycols up to 1000 to2000 molecular weight. The most popular glycols for the manufacture ofester lubricants appear to be polypropylene glycols having a molecularweight of about 100- 300 and 2-ethyl hexanediol. The 2,2-dimethylglycols, such as neopentyl glycol have been shown to impart heatstability to the final blends. iinor amounts of other glycols or othermaterials can be present as long as the desired properties of theproduct are not unduly deleteriously affected. Aside from glycols, theesters may be made from polyhydric alcohols of more than two hydroxylgroups, e.g. tri and tetra hydroxy aliphatic alcohols having about 4 to12 carbon atoms, preferably about 5 to 8 carbon atoms, for instance,pentaerythritol, trimethyloipropane and the like. Particularly suitableester base oils are formed when these alcohols are reacted withmonocarboxylic acids having about 4 to 12 carbon atoms, preferably 4 to9 carbon atoms. It is preferred that the reaction be conducted so as tocompletely esterify the acids.

()ne group of monocarboxylic acids includes those of 8 to 24 carbonatoms such as stearic, lauric, etc. The dicarboxylic acids employed inmaking ester lubricants will in general contain from about 4 to 12carbon atoms. Suitable acids are described in US. 2,575,195 and includethe aliphatic dibasic acidsof branched or straight chain structureswhich are saturated or unsaturated. The preferred acids are thesaturated aliphatic dicarboxylic acids containing not more than about 12carbon atoms, and mixtures of these acids. Such acids include succinic,adipic, suberic, azelaic, and sebacic acids and isosebacic acid which isa. mixture of a-ethyl suberic acid, 0L.Z.-diethyl adipic acid andsebacic acid. This composite of acids is attractive from the viewpointof economy and availability since it is made from petroleum hydrocarbonsrather than the natural oils and fats which are used in the manufactureof many other dicarboxylic acids, which natural oils and fats arefrequently in short sup ply. The preferred dibasic acids are sebacic andazelaic or mixtures thereof. Minor amounts of adipic used with a majoramount of sebacic may also be used with advantage.

Various useful ester base oils are disclosed in United tates PatentsNos. 2,499,983; 2,499,984; 2,575,195; 2,575,196; 2,703,811; 2,705,724and 2,723,286. Generally the synthetic base oils consist essentially ofcarbon, hydrogen and oxygen, i.e. the essential nuclear chemicalstructure is formed by these elements alone. However, these oils may besubstituted with other elements such as halogens, e.g. chlorine andfluorine. Some representative components of ester lubricants are ethylpalmitate: ethyl stearate, di-(Z-ethylhexyl) sebacate, ethylene glycoldi-laurate, di-(Z-ethylhexyl) phthalate, di(1,3-methylbutyl) adipate,di-(2-ethylbutyl) adipate, di-(l-ethylpropyl) adipate, diethyl oxylate,glycerol tri-n-octoate, dicyclohexyl adipate, di-(undecyl) sebacate,tetraethylene glycol-di(ethyleno hexoate), diceliosolve phthalate, butylphthallyl butyl glycolate, di-n-hexyl fumarate polymer, dibenzylsebacate, and. diethylene glycol bis(2-n-butoxy ethyl carbonate).2-ethylhexyladipate-neopentyl glycyladipate-Z-ethylhexyl, is arepresentative complex ester. Generally, these synthetic esterlubricants have a viscosity ranging from light to heavy oils, eg. about50 SUS at F. to 250 SUS at 210 F, and preferably 30 to SUS at 210 F.

The esters are manufactured, in general, by mere reaction of thealcoholic and acidic constituents, although simple esters may beconverted to longer chain components by transestcrification. Theconstituents, in the proportions suitable for giving the desired ester,are reacted preferably in the presence of a catalyst and solvent orwater entraining agent to insure maintenance of the liquid state duringthe reaction. Aromatic hydrocarbons such as xylene or toluene haveproven satisfactory as solvents. The choice of solvent influences thechoice of temperature at which the esterification is conducted; forinstance, when toluene is used, a temperature of 140 C. is recommended;with xylene, temperatures up to about 195 C. may be used. To provide abetter reaction rate an acid esterification catal st is often used. Manyof these catalysts are known and include, for instance, HCl, H 50 NaHSOaliphatic and aromatic sulfonic acids, phosphoric acid, hydrobromicacid, HF and dihydroxyfluoboric acid. Other catalysts are thionylchloride, boron trifluoride, and silicon tetrailuoride. Titanium estersalso make valuable esterification and tr-ansesterification catalysts.

In a preferred reaction, about 0.5 to about 1 weight percent, oradvantageously, 0.2 to 0.5% of the catalyst is used with a xylenesolvent at a temperature of to 200 C. while refluxing water. Thetemperatures of the reaction must be sufficient to remove the water fromthe esterification mass as it is formed. This temperature is usually atleast about 140 C. but not so high as to decompose the Wanted product.The highest temperature needed for the reaction will probably be about200 C., preferably not over about C. The pressure is conveniently aboutatmospheric. Although reduced pressure or superatmospheric pressurecould be utilized, there is usually no necessity to use reducedpressurcs, as the temperatures required at atmospheric pressure toremove the water formed do not usually unduly degrade the product.

When reacting glycols with dibasic acids to produce a polyester, it ispreferred to continue the reaction with concomitant boiling off of waterfrom the reaction mixture until the polyester product has a kinematicviscosity of about 15 to 200 centistokes at 210F., preferably about 40to 130 centistokes. When this point has been I reached, thepolymerization can be-stopped, for instance,

by adding a capping alcohol to'the reaction mixture, and continuing areflux until Water ceases to be evolved. The capping alcohol is a lowmolecular weight monoalcohol of up to about 20 carbon atoms. It isstandard practice, when esters are made using the conventional acidcatalysts such as sodium bisulfate or paratoluene- :sulfonic acid togive the esters an after-treat by washing the ester with a 5 percentaqueous K CO solution or by heating the ester in an autoclave for 15hours at 340 to 350 F. with weight percent of propylene oxide. It isalso conventional to subject the ester to filtration to re moveinsoluble materials. After this the product may be 6 EXAMPLE II Parts bywt. Plexol-255 1 97.75 Phenothiazine 0.5 Glycol titanate 2 0.25 Sebacicacid I .0075 D.C.F ZOO-60,000 .001 5-ethyl-10,10 diphenylphenazasiline1.0

A mixture ofdiisooctyl adipate, di-tridecyl sebacate, and

EXAMPLE III subjected to a reduced pressure distillation or strippingPartsby wt. at 100 to 200 C. to remove volatile materials, such asDllsooctyl fi at 25.5 Water, the solvent, and light ends. -1 f 1 73.0Samples of ester fluids without an oxidation inhibitor Ph@n0ih1aZ 1ne0.5 and samples containing phenothiazine alone, S-ethyl-lO, FreeflZelalC acid 0.01 10 diphenyl phenazasiline alone and samples made ac-,0 0 0.001 cording to the present invention containing varying pro- Y Jdlphenylphenazasflme 1.0 portions Of 5-ethyl-10,10 diphenylphenazasilinea Derived from the reaction of one mole of neopentyl glycol,phenothiazine were Subjected to oxygemabsorpfion tests 2 moles ofazelaic acid and two moles of isooctyl alcohol. The tests were conductedat 450 F. by passing a stream We claim: of oxygen at the rate of onecubic foot per hour through 1. A lubricant composition consistingessentially of an 75 grams of the ester fluid containing the inhibitorsand ester-based fluid of lubricating viscosity and minor comparing theamount of oxygen absorbed vs. time. amounts effective to retardoxidation at temperatures in The induction period is signalled by amarked increase excess of 400 F., of about .01 to 5 percent by weight ofin the rate or" oxygen absorption. The results of these phenothiazineand about .01 to 5 percent by weight of tests are shown in Table I.5alkyl-10,1O diphenylphenazasiline wherein the alkyl TABLE I Results ofOxygen Absorption Tests 7 [Oonditionsz 450 F.; 1 its O2/hr.; 75 g.fluid] Cone. Induction Total Volume Run No. Name Additives (wt.perperiod time 038 abfluid cent) (min) (min) sorbed 5 119 3, 000 117 1462, 500 205 247 2,500 5-ethyl-10, 10 (111] 5 47 2, 500

phenazasiline. Phenothiazine 0 5 304 do. 5-ethyl-l0,10-d1phenyl- 319 3882,500

phenazasiline.

An ester from pentaerythritol and a mixture of aliphatic monocarboxylicacids with an average chain length of seven carbons.

The lengths of the induction periods serves as a significant measure ofthe relative effectiveness of the inhibitors. As shown in Table I, the5-ethyl-l0,10 -diphenylphenazasiline-phenothiazine synthetic ester-basedlubri-.- cant composition prevents oxygen uptake by the fluid for morethan twice as long as would be expected from the results obtained whenusing phenothiazine and 5-ethyl- 10,10 diphenylphenazasiline alone.

Other examples of formulations made in accordance A diethylhexylsebacate oil having a. kinematic viscosity at 100" F. of 12.3 cs., aviscosity index of 154-, a pour pomt of below -80 F. and acid No. of0.12.

2 A polymer derived from tetrabutyl titanate and 2-ethy1-1,3-hexanediol.

D.C.F. 20060,000 is a methyl silicone polymer havmg a viscosity of60,000 cs. at 25 C. and is an anti-foaming agent.

group contains 1 to 4 carbon atoms, said ester-based fluid being anester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylicacid of 4 to 12 carbon atoms.

2. The lubricant of claim 1 containing about 0.1 to 2 percent ofphenothiazine, and about 0.1 to 2 percent by weight of 5-ethyl-10,10diphenylphenazasiline.

References (Iited in the file of this patent UNITED STATES PATENTSFainman Aug. 23, 1960 Kock May 22, 1962 OTHER REFERENCES Cohen,'-et al.:Aliphatic Esters, I and E Chem., vol. 45, No. 8, August 1953, pp.1766-1775.

Dintses et al.: Synthetic Lubricating Oils, published by LiaisonOtiices, Technical Information Center, Wright Patterson AFB, Ohio,F-TS-9719/V, August 1959, pages 283-304.

Rodd: Chemistry of Carbon Compounds, Vol. No (1960), page 1519, QD, 251,R6.

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF AN ESTER-BASEDFLUID OF LUBRICATING VISCOSITY AND MINOR AMOUNTS EFFECTIVE TO RETARDOXIDATION AT TEMPERATURES IN EXCESS OF 400*F., OF ABOUT .01 TO 5 PERCENTBY WEIGHT OF PHENOTHIAZINE AND ABOUT .01 TO 5 PERCENT BY WEIGHT OF5-ALKYL-10.10 DIPHENYLPHENAZASILINE WHEREIN THE ALKYL GROUP CONTAINS 1TO 4 CARBON ATOMS, SAID ESTER-BASED FLUID BEING AN ESTER OF AN ALKANOLOF 4 TO 12 CARBON ATOMS AND AN ALKANE CARBOXYLIC ACID OF 4 TO 12 CARBONATOMS.